Is St. Louis County, MO in a flood zone?
FEMA's National Risk Index puts St. Louis County's flood hazard at the 99.1th percentile nationally — well above the national norm for flood hazard — driven by inland rivers and flash flooding rather than the coast — FEMA's model puts a flood event here at about 2.8 times a year. County-wide, not parcel-specific: FEMA's real flood-zone map is queried live, never shipped as a download.
Mandatory flood insurance compliance in St. Louis County
Homes with a federally backed mortgage inside St. Louis County's mapped high-risk flood zone (the Special Flood Hazard Area, or SFHA) are legally required to carry an NFIP flood policy. In practice, 34% of them do — 1,178 active policies against 3,470 structures FEMA counts in that zone, leaving a real compliance gap. Across all residential structures in St. Louis County, not just the ones FEMA mandates, 0.6% carry an NFIP policy — most flood damage nationally happens outside the mapped high-risk zone, so that broader number matters too.
How St. Louis County compares nationally
St. Louis County sits at rank 33 of 3144 counties on FEMA's flood hazard scale (1 is worst) and rank 52 of 3144 by population (1 is biggest). St. Louis County, Missouri is home to about 992,929 people across 508.525 square miles of land.
Checking a specific address in St. Louis County
2,070 of St. Louis County's 360,986 residential structures carry flood coverage of some kind, per FEMA's latest count — useful context, not a substitute for checking one parcel.
More on how this number was built
The methodology guide shows exactly which FEMA and Census tables feed St. Louis County's numbers. The guide to what the Special Flood Hazard Area actually means explains why the mandatory-insurance rule exists and who it applies to.